384 MOLLUSCA SUB-KINGDOM VI 
Superfamily 8. ANOMIACEA. Herrmannsen. 
Shell monomyarian, not alate ; edentulous or Isodont, usually sessile ; shell substance 
nacreous, tubuliferous, with traces of a prismatic layer ; area obscure, usually small, 
amphidetic ; ligament obscure, with an alivincular internal resilium ; gills filibranchiate, 
mantle lobes free ; foot small, grooved, digitiform ; dioecious ; marine. 
Family 37. Anomiidae. Gray. 
Shell variable, irregular and inequivalve when sessile, byssiferous when young ; in 
most genera the byssus becomes modified to a calcified or horny plug passing through a 
foramen in the attached valve, and fastened to other objects, a condition which may be 
permanent or transient; area small, amphidetic ; ligament amphidetic, more or less 
internal, supplemented by an internal resiliwm, for which the crura serve as chondrophores, 
ali- or multivincular ; hinge usually edentulous, rarely rugose, with amorphous inter- 
locking rugosities ; posterior adductor small, sub-central, in the sessile forms reinforced by 
the pedo-byssal muscles, which are modified for service as adductors. ? Devonian. Jura 
to Recent. 
Anomia, Mill. Shell thin, sessile by the calcified byssus passing through a sinus 
or perforation in the right valve, conforming to the subjacent surface; the left valve 
more convex, with four muscular scars on 
a central area; a chondrophore in the 
lower valve. Jura to Recent. 
; Z ?Limanomia, Bouch. Devonian. 
SES Hypotrema, VOrb. Jura and Cretaceous. 
7 a Placunanomia, Brod. Miocene to Recent. 
Carolia, Cant. (Fig. 676). Shell 
orbicular, compressed, radially striated ; 
right valve with a byssal foramen nearly 
closed in the adult; resilium much as in 
Anomia ; adductor scar single. Eocene ; 
Egypt. 
Sub-genus: Wakullina, Dall. Smooth ; 
byssal foramen obsolete ; the resilium received 
on diverging crura in the upper valve. Oligo- 
cene ; Florida. 


Za 
Placenta, Retzius (Placuna, Brug.; 
Placunema, Stol.; Pseudoplacuna, Mayer). 
Shell free, orbicular, thin, very compressed ; 
the resilum with long, unequal crura. 
Tertiary and Recent. 
Ephippium, Bolten. Like Placenta, 
but the shell radially waved ; young with a small byssal perforation, which becomes 
closed and obsolete in the adult. Tertiary and Recent. 
Placunopsis, Morr. and Lye. Shell rounded, imperforate, free, or sessile. Jura. 
Hemiplicatula, Desh. (Semiplicatula, Fisch.); Saintia, Raine. Eocene. Paranomia, 
Conrad. Ripley Group. Monia, Gray. Miocene ; California. 
Fic. 676. 
Carolia placunoides, Cantr. Eocene; Wadi el Tih, 
near Cairo, Egypt. Interior of both valves, 2/3. 
V. Dysoponra. Neumayr (emend.) 
Superfamily 9. MYTILACEA. Ferussac. 
Shell anisomyarian, usually equivalve, not alate or notched for a byssus, edentulous 
or Dysodont ; shell substance sub-nacreous, rarely more or less prismatic, with a conspicu- 
